Preparation of Al₂O₃ from the Nepheline Ore of Nanjiang County, Sichuan Province of China

Abstract

Crystalline alumina samples with Al2O3 content of 95.23 wt.% were prepared directly from the nepheline ore in Nanjiang county, Sichuan province of China. Four steps were involved in the experiment of alumina preparation, including calcination, dissolution, carbonation and re-calcination. Lime was used in the calcination process with the nepheline concentrates powders to generate soluble aluminates and insoluble silicates. NaOH solution was used as the mother solution in the dissolution process. CO2 was introduced into the solution to precipitate the Al (OH)3 precursor, which was then fired to obtain crystalline alumina. Among the crystalline alumina obtained three phases of crystals existed which were detected by XRD and SEM, including δ-Al2O3 as the major phase, while θ-Al2O3 and κ-Al2O3 as the minor phases. Various crystal phases of alumina could be ascribed to the purity and crystal structure of precursor, as well as the re-calcination temperature and time.